dimension and ornamental stones from the tosco-romagnolo...

ABSTRACT. — The hilly territory of the easternEmilia-Romagna up to the Apennine watershed, alsocomprising part of the Romagna Toscana, representsin Italy the main sandstones producer, along with thePietra Serena of Firenzuola and Marradi and thePietra Serena from the Savio valley. Minor districts,not less important for the local economy are alsopresent, such as those exploiting the seleniticgypsum of Brisighella, Borgo Rivola, BorgoTossignano, Bologna and the «CrystallineAlabaster» of Torriana, the San Marino calcarenites,the Montefeltro limestone and the Montovolo andCastel d’Aiano sandstones. We should not forget thehistorical-cultural heritage constituted by the nowdismissed quarries of the Varignana, Sasso Marconi,Monghidoro, Castiglione dei Pepoli and Porrettasandstones, employed since the Villanovian,Etruscan, Roman, Medieval and Renaissance ages;as well as unique materials, locally employed, suchas the Montecodruzzo limestone, the Spungonecalcarenite, the Labante travertine, the euphotidegabbro and the Mantesca and San Zanobiserpentinites.

The aim of the authors is to give in this worksome historical elements of knowledge ondimension and ornamental stones and not to putforward a research work regarding the geology andstratigraphy of the area.

RIASSUNTO. — Il territorio montano e collinaredell’Emilia orientale e della Romagna fino allospartiacque appenninico, comprendente anche partedella Romagna Toscana, rappresenta, in camponazionale, il maggior produttore di arenaria con laPietra Serena di Firenzuola e di Marradi e con laPietra Serena della Val Savio. Sono altresì presentiminori realtà produttive ma non meno importantinell’economia locale come quelle dei gessi seleniticidi Brisighella, Borgo Rivola, Borgo Tossignano,Bologna e dell’«Alabastro Cristallino» di Torriana,della calcarenite di San Marino, del calcare delMontefeltro e delle arenarie di Montovolo e diCastel d’Aiano. Non va dimenticato il patrimoniostorico-culturale costituito dalle cave ora dismessedelle arenarie di Varignana, di Sasso Marconi, diMonghidoro, di Castiglione dei Pepoli e di Porretta,impiegate già in epoca villanoviana, etrusca,romana, medioevale e rinascimentale. Nonché dimateriali unici di impiego locale come il calcare diMontecodruzzo, la calcarenite dello Spungone, iltravertino di Labante, il Gabbro eufotide e leSerpentiniti della Mantesca e di San Zanobi.

Lo scopo principale degli autori non è quello direalizzare un lavoro di ricerca riguardante lageologia e la stratigrafia della zona presa inconsiderazione bensì quello di fornire alcunielementi storici di conoscenza sui materiali lapideiornamentali e da costruzione.

KEY WORDS: Dimension and ornamental stones,quarries, petrography, employment.

Per. Mineral. (2004), 73, 171-195 http://go.to/perminSPECIAL ISSUE 3: A showcase of the Italian research in applied petrology

Dimension and ornamental stones from the Tosco-Romagnolo and Bolognese Apennine

GIUSEPPE MARIA BARGOSSI1*, FABIO GAMBERINI1, GIORGIO GASPAROTTO1, GIAN CARLO GRILLINI2 and MARTA MAROCCHI1

1 Dipartimento di Scienze della Terra e Geologico-Ambientali, P.zza di P.ta San Donato, 40126 BolognaAlma Mater Studiorum Università di Bologna

2 Geologo specialista libero professionista, via Weber, 2-Bologna

* Corresponding author, E-mail: [email protected]

An International Journal ofMINERALOGY, CRYSTALLOGRAPHY, GEOCHEMISTRY,ORE DEPOSITS, PETROLOGY, VOLCANOLOGYand applied topics on Environment, Archaeometry and Cultural Heritage

INTRODUCTION

The territory located on the eastern side ofthe Emilia-Romagna region, in the areabounded by the via Emilia axis and the Tosco-romagnolo Apennine ridge, preservesevidences of stone employment which since theVillanovian age are coming up to nowadays.All the different populations and cultures whoinhabited these regions following one another,have found in the stone a proper material bothto put into effect artistic and religiousexpressions and to build public and privateworks. The presence of stone materials in a citynormally represents the synthesis betweenbuilding stones occurring in the hinterland androcks which have been imported even fromvery far places. They indifferently andpowerfully fulfil both aesthetic tasks andstructural requirements.

As far as we consider the cities examined inthis paper, from Bologna to Imola, Faenza,Forlì, Cesena up to Rimini, the most commonbuilding materials are sandstones, selenites andlimestones, coming from nearby quarries andtherefore easy to be found with reasonablepurchase and transportation costs. Besidesthese «poor» materials, stones coming from theVenetian and Istrian quarries are harmoniouslyassociated. The thick canal network connectingthese cities to the Adriatic sea and to the Poriver, together with the via Emilia and Romea,made it possible for these materials to bebrought in large amounts and then employedmainly in factories with «very rich economy»and in important public buildings. As statedbefore, these were very expensive materials;we should remember that such an importantsite as San Petronio, wanted by all the cityinhabitants and by the powerful artcorporations of Bologna, was never completed,not even the façade covering, due to the highmaterials’ costs, here, more precisely, referringto the Istrian stone, to the white and redlimestones from Verona and to the Candogliamarbles. To the stone, employed in portals, inarchitectural frameworks, in capitals, in carvedcornices, in doors and windows fastigia, was

attributed the duty of underlining the elegance,the nobility or importance of a building. Theseemployment criteria had an even strongerimportance on minor buildings, where thebuilding ordinary character did not imply andjustify a dismissal of the usual procedure.Therefore, the stone employment was restrictedto a few and precise architectural elements inbuilding prospects, such as corner parastades,coats-of-arms or decorative elements of somekind of importance.

Mainly referring to and taking inspirationfrom the famous work by Rodolico (1953) «Lepietre delle città d’Italia» and restricting thistreatment to the territory previously described,our principal aim was collecting elements ofgeological, petrographic and mineralogicalknowledge, together with the employment oflocally mined dimension stones, and toinvestigate the deterioration phenomena thesematerials have suffered since they have beenemployed in the urban environment. We thinkthat the arguments we collected in this papercould help earth scientist and cultural heritageestimators to better understand the relationshipexisting between these cities and thesurrounding land, and that a careful utilizationof georesources can produce a generalenrichment both economic and cultural.

LIST OF ORNAMENTAL STONES: GEOLOGY,PETROGRAPHY AND HISTORICAL EMPLOYMENT

The terrains outcropping in the investigatedarea (Fig. 1) are mainly represented by clasticsedimentary rocks and subordinately byevaporitic and carbonatic rocks while only avery small part consists of ophiolites.

The rocks which have been mined in the pastand are nowadays mined in the active quarriesof the Santerno and Savio river valleys,represent an important georesource for thesemountain territories; they will be describedaccording to a chronological order referring tothe geological age of the belonging formation(Società Geologica Italiana, 1990).

G.M. BARGOSSI, F. GAMBERINI, G. GASPAROTTO, G.C. GRILLINI and M. MAROCCHI172

Dimension and ornamental stones from the Tosco-Romagnolo and Bolognese Apennine 173

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A) The Sasso della Mantesca gabbros andserpentinites (Bologna)

GEOLOGICAL SETTING

Gabbros and serpentinites belonging to theVara Supergroup ophiolites (external LigurideDomain), of Jurassic age, outcrop between theIdice and Sillaro river valleys scattered in theundifferentiated Chaotic Complex betterknown as «Argille Scagliose». These rocks,much more compact than the highly disruptedclays which include them, give rise to smallrelieves called «Sasso della Mantesca» and«Sasso di San Zanobi» (Grillini, 1977).

MINING ACTIVITY

Mining activity in the «Sasso dellaMantesca» area in the watershed from theSillaro and Idice valleys has gone on until 1940and regarded the well known «euphotide»Gabbro, the «ranocchiaia Serpentinite» and the«serpentinitic Breccia».

MINERALOGICAL-PETROGRAPHIC CHARACTERS

Euphotide Gabbro

It’s a grey-greenish gabbro, coarse-grained(up to some centimetres) with granularhypidiomorphic structure made up of albitizedplagioclase crystals in which prehnite andchlorite plagues and veins, clay minerals’granulations and strongly foliated, oftenchloritized and serpentinized clinopyroxene(diallage) are present. Relicts of totallyserpentinized olivine have also been detected.The main accessory phases are represented byilmenite, hematite and apatite (Fig. 2).

Serpentinites

They show cellular structure with largebastite aggregates in parallel and shininglamellae (lizardite) replacing the originalorthopyroxene, embedded in a matrix made upof finer-grained serpentine and magnetitegranulations (Fig. 3). Sometimes the rock ismore or less intensively brecciated and re-cemented by the presence of yellow-light

green-coloured chrysotile filling fractures andveins with a typical fibrous disposition whichis perpendicular to the veins’ elongation. The«ranocchiaia» variety looks massive, withopaque magnetite which gives rise to orientedlineations embedding yellowish lizardite eyes.Chrysotile with a typical fibrous aspect in lightveinlets scattered in a blackish matrix can alsobe observed. This ophiolitic lithotype


Fig. 2 – Photomicrograph of euphotide gabbro (Sasso dellaMantesca); the lower part is made up of serpentinizedclinopyroxene diallage, the upper part of albitizedplagioclase (N//).

Fig. 3 – Photomicrograph of serpentinite (Sasso dellaMantesca) showing the typical cellular structure (N//).

frequently outcrops in the Ligurian-Emilian (LaSpezia, Parma, Reggio Emilia, Bologna),Tuscan (the so called «Verde di Prato»)Apennine and in the up Tiberina Valley nearbyAnghiari and Pieve Santo Stefano.

Serpentinitic Breccia (Ophicalcite)

It is a breccia made up of green blackish-coloured serpentinite fragments bounded by avery thick calcite veins network (Fig. 4).Among the serpentinite fragments thepreviously described serpentine varieties andchrysotile veins fragments are bothrepresented. Calcite is commonly coarse-grained, often occurring in isoriented crystalsforming fibrous aggregates whichcrystallization is perpendicular to the veinselongation.

HISTORICAL AND PRESENT-DAY EMPLOYMENT,DETERIORATION AND PRESERVATION

Euphotide Gabbro

The main employment of euphotide gabbroscan be found in millstones along the Idiceand Reno valleys in the Bologna province. Thisarchitectural material, with structural

employment, can be found in Bologna in the «Palazzo della Questura» basis (1934), in road paving under the «Torresotti» circledoor in Via Castiglione and in the externalgarden basal part of the «Stefaniano» Complex.

The typical coarse-grained structure and inparticular the diallage pyroxene, oftenserpentinized and chloritized with evidentcleavage planes, cause a selective deteriorationwith a deep rock disruption.

Serpentinites

The employment in Roman age isdocumented but limited; a great diffusionoccurred in Romanic, Gothic and Renaissanceage in Toscana and Liguria, defining thecharacteristic «pisano or toscano style» ofRomanic churches with decorations alternatingpolychrome light and dark marbles. Theapplication, mainly ornamental, in mirror-looking altars’ surfaces, cartouches, smallcolumns and both wall and paving mosaictarsia, arises from and is justified by itsbeautiful dark green colour.

The main deterioration morphologies,characteristic of this lithotype, are representedby a chromatic alteration revealed by a colourvariation, turning into a grey-greenish, and by apartial disaggregation with detachment ofbastite and lizardite crystals from themagnetite-formed groundmass, underminimum mechanical stress. The chrysotile,talc and calcite veins, occurring in particular inthe serpentinitic breccia, can cause a thick netof cracks and preferential detachment surfacesto be produced.

B) The Monghidoro Sandstone (Bologna)

GEOLOGICAL SETTING

The Monghidoro Sandstone (Arenarie diMonghidoro) belongs to the external Liguridedomain (Sambro Supergroup). This Formationsigns the gradual change from the alternation ofcalcareous-marly and arenaceous-shalyturbidite successions from the underlying


Fig. 4 – Photomicrograph of serpentinitic breccia(ophicalcite), Sasso della Mantesca. Serpentinite fragmentscemented by a very thick calcite network (NX).

Monte Venere Formation (Maastrichtian-Paleocene) towards arenaceous turbiditesedimentation with a different sand/clay ratio,characteristic of both abyssal plain and outerfan environments. The top of the Formation isdated Upper Paleocene.

MINING ACTIVITY

The Monghidoro sandstones have beenquarried near the Monghidoro village wherethree arenaceous horizons, dipping more or lessparallel to the slope, are mined in the «Balzidel Carlino» quarry. The lower bed, about onemeter thick, and the upper one about 50 cmthick are inter-divided by siltitic-muddy levels,show direct gradation (thinning upward) andare lamination free. Also in the localityCanovetta di Sopra near the S. Andrea ValSavena village these sandstones have beenmined in the Canovetta quarry from anarenaceous horizon of about one meter mediumthickness, dipping parallel to the slope withslight inclination, gradated and clearlylamination free.


The Monghidoro sandstones are classified asarkoses passing into lithic-arkoses, showcolour ranging from light grey to yellowishand grainsize ranging from coarse to fine (Fig.5). The siliciclastic component is dominant,with clasts of quartz, feldspars (orthoclase,plagioclase and microcline in abundancedecreasing order), micas (muscovite, biotiteand chlorite), igneous rocks fragments(haplites and acidic vulcanites) and rarelymetamorphic rocks fragments (gneiss). Thequartz-feldspar clasts present subangular lowersphericity morphology, while thephyllosilicates show a platy one. Carbonaticrocks fragments are quantitatively subordinate;they are micritic and spatitic limestones withellipsoidal morphology and curved rims.Accessory phases are mainly made up ofopaque minerals (framboidal pyrite) andtransparent minerals such as zircon and garnet.

The interstitial matrix among the clasts isfilled by the siltitic component and by thespatitic carbonatic cement. The clasticcomponent all together reveals a strongtendency towards the development of a sub-parallel isorientation with respect to thesandstone sedimentation plane, withoutformation of any level characterized byselective concentration.


Mining was carried out with artisan methodsusing hammers and wedges exploiting the rockveins; the caved material was used in loco forthe construction of villages (with thecharacteristic tower-houses), of rural housesand for road paving.

The Monghidoro Sandstone neverthelesshaving a medium imbibition’s coefficient,shows, in the observed employments, an easyattitude to flaking and to the transformationinto sand since it is particularly sensitive to thewater disruption effect. Materials at workwhich display particular sedimentarystructures, such as laminations or grain sizeheterogeneities, can cause after some time adifferential deterioration with exfoliations andpreferential detachments.


Fig. 5 – Photomicrograph of lithic arkose (Monghidoro)with main quartz-feldspars component (N//).

c) The Castiglione dei Pepoli Sandstone(Bologna)

GEOLOGICAL SETTING

The Castiglione dei Pepoli Stone also calledMonte Baducco Sandstone (Arenaria di MonteBaducco) belongs to the Miocene (Aquitanian-Langhian) Falterona-Cervarola Formation madeup of quartz-feldspars sandstones, siltstones andclaystones interbedded with thin hemipelagiccarbonatic layers. In the mining areas of MonteBagucci and Monte Gatta an anticlineculmination, of nearly symmetric shape with subvertical orientation of the axial surface, extends.

The compressive tectonic acting in the areahas deeply influenced, during different stages,this structure, which seems to have been deeplydisrupted by multiple tectonic discontinuitiesrepresented by both direct and inverse faults.

MINING ACVITITY

Among all the sandstones’ quarries locatedon the Castiglione dei Pepoli area andabandoned in 1960, the most representative issituated nearby the bridge on «Fosso dellaChiesa Vecchia». The outcrop is made up ofsandstones which colour ranges from grey-bluish to yellow-brown, organized in beds fromdecimetric to metric, interbedded to thin shalylayers. It was used to be mined in terraces and,not withstanding the long neglecting period,the walls are still clean and vegetation free. Thequarry front extends for about 50 meters with afrontal height of about 20 meters.


Mined sandstones are classified as lithic-arkoses and feldspatic litharenites. Thesiliciclastic component is characterized by asubangular morphology with low sphericityindex and is made up of quartz, plagioclase andorthoclase grains (Fig. 6). To this componentalso belong phyllosilicatic clasts, well orientedand sometimes stretched, of muscovite, biotiteand chlorite and polycrystalline rockfragments. Among rock fragments, extrabasinalcarbonatic clasts commonly micritic and

muddy are also present, less frequently spatiticrounded or elongated-shaped with curved rims.The presence of less common glauconite, flintand framboidal pyrite has also been detected.Bioclasts are very scarce. The cement is madeup of clear spatitic calcite.


The Monte Baducco Sandstone has beenemployed in the Castiglione dei Pepoli area asornamental building stone since the XIII-XIVcentury. At first, the employed stone wasobtained by erratic blocks found in reclaimedlands which had been turned into farming. Afterthe XV century the inhabitants were forced, bythe raw material’s shortage and the alreadyactive mining centres’ distance, to mine thestone opening new different borrowing quarriesfrom Monte Bagucci and Monte Gatta areas.

In sandstones employed outdoor, typicaldeterioration morphologies have been observedon surfaces, such as disruption with aconsequent progressive transformation of thematerial into sand. These sandstones, whenemployed in wet, northward-looking placestend to show a strong biologic deteriorationwith green-coloured algal coatings formationand different lichen species colonization, some


Fig. 6 – Photomicrograph of lithic arkose (Castiglione deiPepoli), dominated by a quartz-feldspar component inwhich biotite and chlorite are also present (N//).

of which display strong colours ranging fromgrey to red up to deep yellow.

d) The Porretta Sandstone (Bologna)

GEOLOGICAL SETTING

The Porretta Sandstone (Arenarie diPorretta), presently referred to as Arenarie diSuviana, belongs to the terrigenous turbiditeformations of the Tuscan Domain’s CervarolaGroup. Above the Suviana Marls characterizedby bad-stratified marls and silty-marls, in thePorretta Terme area (Bologna) we pass into thePorretta Sandstones made up of a somehundreds-metres-thick succession of middle-Miocene arenaceous turbidites.

MINING ACTIVITY

The rock was mined from different quarrieslocated south-western of the Porretta Termevillage (Madonna del Ponte, della Costa, dellaPuzzola and di San Rocco); some of thesequarries are no more visible since they havebeen hidden by the new buildings of thethermal resort. The Madonna del Ponte quarry,next to the homonymous church, is the betterpreserved one and makes it possible for thehigh wall, made up of sandstone metricverticalized strata, which total thickness isabout 60 metres, to be observed. In the quarry,where signs left by the past mining activity arestill visible, the sandstone strata outline erosivecontacts and amalgamations with suddengranulometric changes and intraformationalclay inclusions. Lenticular geometries, plane-parallel laminations, groove casts andbioturbations are also present (Agostini, 1994).Moreover, decimetric lithoclases arecharacteristic, with crystallization of calciteand of the famous Porretta’s hopper quartz,filled by yellowish clay.


The «Macigno di Porretta» is a dark grey-coloured, medium-grained lithic arkose, withwhite mica (muscovite) lamellae oriented

parallel to the stratification planes (Fig. 7).From a petrographic point of view, it mainlyconsists of quartz, feldspars and phyllosilicategrains with a minor amount of siliciclasticrocks fragments. A certain amount ofextrabasinal carbonatic clasts is also present.The carbonatic cement generally tends toocclude the interstices among grains.


This sandstone has been widely employed upto the last century in building works realized inPorretta such as the «Madonna del Ponte»church and along the Reno valley up toBologna.

These sandstones, in case of outdooremployment, result particularly sensitive to thedeterioration agents which can give rise tomanufacture decay, sometimes not reversible.The result mainly consists of exfoliations anddetachments caused by inflation, cracking andalong strata fractures, turning into sand andefflorescences.

E) Tthe Bismantova Formation

Montovolo Stone (Bologna)Castel d’Aiano Sandstone (Bologna)


Fig. 7 – Photomicrograph of lithic arkose (Porretta), withabundant quartz, feldspar and phyllosilicate clasts showingan oriented texture (N//).

GEOLOGICAL SETTING

In the Vergato surroundings (Bologna), inthe Reno valley, the lower-middle MioceneBismantova Formation locally referred now toas Bismantova Group belonging to theEpiligurian Domain outcrops. This Formationincludes the Upper Burdigalian-LowerLanghian calcarenites of the Bismantova StoneMember (Montovolo Stone) and the coevalbiocalcarenites and calcareous sandstones ofthe Pantano and Sasso Baldino Members(Castel d’Aiano Sandstone).

MINING ACTIVITY

Montovolo Stone – The two main quarries,both active until few decades ago, are locatedsouthern of Vergato, on Montovolo, and arecalled Vecchi Quarry (Cava Vecchi) andBerardi’s Quarry (Cava dei Berardi). Even fromthe adjoining Monte Vigese, mainly in theGreglio and Cardeda localities, great amountsof sandstones were quarried from blockssloughed from the walls. The stone, in massivestrata up to few metres thick, was mined andworked with traditional manual methodsinherited from the Comacine masters workingin this area during the Middle Ages, of whichremain, as proof, numerous villages with tower-houses and churches (Bargossi et al, 2000b).

Castel d’Aiano Sandstone – The only activequarries of these sandstones, belonging to theSasso Baldino Member, located western ofVergato, are the Furnace Quarry (CavaFornace) and the Evangelists Quarry (CavaEvangelisti) of Rocca di Roffeno nearby Casteld’Aiano. The Evangelisti Quarry, set up on alarge gravitational mass movement, developson bad-defined terraces. In the near zone of theVergato area in the 19th century the quarries of«Spezzola di Sopra» and the «Barelli’sQuarry» were also active, both set up onsandstones belonging to the Pantano Member(Pilone, 2000).


The Montovolo Stone, better known in theliterature as «Ophiolitic Molassa» is a

calcarenite which colour ranges from grey-bluish to yellowish when oxidized and whichgrainsize ranges from fine-medium-grained tocoarse-grained (Fig. 8). It looks massive exceptfor the isoriented disposition of lamellar-shaped minerals and elongated biosomes and alow grade of thickening with a moderateamount of points-like contacts between theskeleton grains. It turned out to be mainly madeup of a bioclastic component represented bybenthonic and plantonic foraminifers’ shellsand also by echinoderms, bryozoans, and algaand bivalves fragments. Fragments of micriticcarbonatic rocks are rarer to be found. Thesiliciclastic component is made up of quartz,feldspars and micas. The matrix made up of acarbonatic cement doesn’t totally obliteratepores and is represented mainly by micritepassing into spatite along the carbonatic clastsgrain boundaries.

The Castel d’Aiano sandstones are grey-blue-coloured calcarenites in the fresh rockpassing into a yellow-brown colour in thealteration zones along litoclases; they show ahomogeneous structure, lamination free,medium-fine-grained with the presence ofbioturbations. Compared to the MontovoloStone, they display a reasonable amount of clayminerals (smectite, illite and kaolinite) which


Fig. 8 – Photomicrograph of the Montovolo stone, acalcarenite characterized by abundant bioclastic component(N//).

concentrate inside the clastic carbonaticextrabasinal component (Fig. 9).


Among works carried out with theMontovolo Stone we remind the «Santa Mariadella Consolazione» Sanctuary, on the top ofMontovolo, of the XIII century, built on theremnants of a more ancient IX-X centuryproto-Romanic church of which only theunderground crypt remains, and the «SantaCaterina d’Alessandria» Oratory, next to theSanctuary, a XIII century Romanic stylechapel. A grey-coloured «molassa» sandstonehas been used as façade covering for the «SantaMaria di Galliera» church in Bologna (1491)and for the two giants supporting the balconyof the XVII century Davia-Bargellini Palace(Rodolico, 1953). More recently the MontovoloStone has been used for the external facing ofthe Government Palace of Bologna (1932-’33),at the present day the police headquarters(Questura), and for the façade covering ofSanta Maria Assunta (Riola), a church of theFinnish architect Alvar Aalto ended in 1978.

The Castel d’Aiano Sandstone, known alsoas Vergato Stone (Pietra di Vergato) or Grey

Sandstone (Arenaria Grigia), has foundemployment in the «Santa Maria di Roffeno»Abbey, consecrated in the XI century, andbetween the XII and the XVI century in tower-houses, towers, parish churches and ruralhouses in the Vergato area.

One of the most beautiful examples ofemployment of the Bismantova Formationsandstones is represented by the «Palazzo deiCapitani della Montagna» covering, a XIV-XVcentury palace in Vergato, rebuilt first in 1885and then after the Second World War (Fig. 10).

The Montovolo Stone, which is characterizedby an imbibition’s coefficient of 1,6%, andeven more so the Castel d’Aiano Sandstonewith a 3,1%, are particularly attacked inoutdoor environment by washing out rains andby rising humidity.

Between the more common deteriorationmorphologies, we can outline visible flakes andpowdered material. The phyllosilicaticcomponent in contact with water swells andspreads freeing the siliciclastic minerals tocreate, in the superficial portions, commondeterioration morphologies such as breaking upand splintering, up to a complete pulverizationof the material.


Fig. 10 – Palazzo dei Capitani della Montagna (Vergato-Bologna). The Palace, now townhall, has been rebuiltduring the post-war period imitating the late nineteenth-century forms in the mullioned windows, in capitals andcolumns. The façade, where the original coats-of-arms ofXIV and XV centuries’ captains are placed, has beenrealized employing the Bismantova Formation Sandstones.

Fig. 9 – Photomicrograph of the Castel d’Aiano Sandstone.Calcarenite characterized by abundant bioclasticcomponent, finer-grained compared to the Montovolostone, and by a dusty micritic cement into which clayminerals have also been detected (N//).

F) The San Marino Formation

San Marino Sandstone (San MarinoRepublic)

Montefeltro Limestone (Pesaro-Urbino)

GEOLOGICAL SETTING

In the area of Romagna and Marche theEpiligurian Domain is characterized in the lateBurdigalian to Langhian by the deposition in aplatform environment of the San MarinoFormation, equivalent to the BismantovaFormation. This Formation presents at the bottomshallow marine deposits with biocalcirudites,passing into massive organogenous limestonesand at the top into calcarenites with obliquestratification and increasing in the siliciclasticcomponent which characterizes theoverhanging Monte Fumaiolo Formation.

MINING ACTIVITY

The Monte Titano area has been the object ofan intense mining activity and local stoneworking since the stone-cutter San Marino,native of Arbe in Dalmatia, took refuge thereduring the Diocletian Empire. Nowadaysboulders and blocks of the San MarinoSandstone are mined, obtained by sawing inbuilding excavations made in the San MarinoRepublic territory. The Montefeltro Limestoneof the San Marino Formation is mined in ValMarecchia in the Le Ceti quarry in Santa MariaMaddalena, Novafeltria (Pesaro-Urbino).


The San Marino Sandstone are whitish andyellowish calcirudites, bryozoans, corals,echinoids and bivalves rich with a minorquartz-feldspar siliciclastic component andwith scarce carbonatic cement giving the rock avery high porosity (Fig. 11).

The Montefeltro Limestone is a pseudo-nodular organogenous limestone brown-yellowish-coloured with greenish and ash-coloured spots. They are made up of anorganogenous component similar to that of theSan Marino Sandstones, without siliciclastic

component and very good cementation madeby micritic and spatitic calcite obliteratingpores (Fig. 12).


The San Marino Sandstone has found largeemployment mainly in the city of Rimini. Inthe Romanic-gothic «Arengo Palace» ofCommunal age, the basis and capitals of pillarsare built in San Marino Sandstone. Thissandstone finds also employment in the string-


Fig. 11 – Photomicrograph of the San Marino Sandstone,laminated calcarenite showing alternation of bioclastic andsiliciclastic levels (N//).

Fig. 12 – Photomicrograph of the Montefeltro limestone,an organogenous limestone (N//).

course of the XVI century Palazzo Lettimi, inPalazzo Garampi decorations and partly in thecovering of Sant’Antonio little temple. Also inthe XVI and XVII century we can observe theemployment of these sandstones in theBonadrada and Gioia Palaces. In theRenaissance monuments wanted bySigismondo Malatesta, in the central arc of thefaçade and in some parts of the MalatestianTemple covering, Leon Battista Alberti usedthe Montefeltro Limestone mined in theVerucchio and Scorticata quarries in ValMarecchia (Rodolico, 1953).

As far as we consider the deterioration ofthese materials, it looks clear that the SanMarino Sandstone, when employed outdoor,tend to turn into sand since it is bad cementedwhile the Montefeltro Limestones due to theirpseudo-nodular structure can give rise to stoneelements’ detachment in correspondence ofinter-nodular sutures.

G) The Marnoso-arenacea Formation

Pietra Serena, Pietraforte Colombino,Albarese

GEOLOGICAL SETTING

The Marnoso-arenacea Formationsandstones belong to the Umbro-RomagnoloDomain. This formation represents the fillingof an Apennine foredeep basin, whichdeveloped between Langhian and Tortonian.The filling of this basin is made up of turbiditesmainly produced by Alpine clasticcontributions from N-NW associated tocarbonatic platform contributions from SE andto mixed types ones from the South-WesternApennine relieves. Litharenites strata ofterrigenous origin (the dominant lithotype),intrabasinal origin strata made up ofcalcarenites (Colombine) and mixed originstrata made up of hybrid arenites (Contessatype) have been distinguished.

In the Firenzuola district, the first stratumimportant in order to be mined is the Contessaone, the more characteristic guide layer of theMarnoso-arenacea Formation, which has been

called by quarrymen Colombino in theSanterno valley and Albarese in the Saviovalley in the Forlì-Cesena province. Anotherlayer called Masso Grosso lies about 700-800meters above the underlying Contessa layer.After about one hundred meters of turbiditicstrata which can’t be exploited, we encounter aseries of strata called Filaretti, which are tradedtogether with the Masso Grosso and called withthe generic name of Pietra Serena.

MINING ACTIVITY

In the Firenzuola area, mining activity hasdeveloped since the XV century and continuedup to the 60s in quarries located along theSanterno river-bed nearby Molino Tinti andMolino Pianaccia. The incoming of modernmining technologies has brought about anenormous increase in the mining activity whichhas nowadays gained remarkable quotationsboth in the national and international markets.The mining basins located in the Firenzeprovince, where actually the Pietra Serena diFirenzuola sandstones are mined and worked,are situated north-western of an uninhabitedvillage called Brento Sanico, in the Rovigotorrent valley, in Peglio, along the Diaternatorrent, in Giugnola nearby Piancaldoli and inPalazzuolo sul Senio (Bargossi et al., 2002b).On the other hand, in Marradi are minedsandstones called Pietra Serena di Marradi.

The Pietraforte Colombino is actually minedNE of Firenzuola in Tirli locality, next to theabandoned village of Colcedra di Tirli.

In the Forlì-Cesena province, in the TorrentPara mining basin, in Mazzi locality andnearby Alfero, sandstones called Albarese andPietra Serena della Val Savio are actuallymined (Bargossi et al., 2000a). Even betweenthe Montone and Bidente valleys in Galeata,sandstones belonging to the Marnoso-arenaceaFormation have been mined in the past.


Sandstones called Pietra Serena show fine-medium grainsize and grey-bluish colour, withwhite mica lamellae (muscovite) which are


arranged parallel to the stratification planes andgive rise to silvery reflexes along surfacesworked by natural split or on «al verso» cutslabs. The finer-grained varieties caneventually display centimetric laminations.From a petrographic point of view, thesesandstones have been classified in the lithicarkoses, feldspatic litharenites and litharenitescompositional fields. They are mainly made upof quartz, feldspar and phyllosilicate grainstogether with minor amounts of siliciclasticrock fragments (Fig. 13). Moderate amounts ofextrabasinal carbonatic clasts and rareintrabasinal bioclasts are also present. Thecarbonatic cement, mainly spatitic andsubordinately micritic, tends to obstruct theinterstices between grains, creating lithotypescharacterized by a roughly modest imbibitioncoefficient ranging from 1,2 to 2,3%.

Sandstones known as Colombino andAlbarese, medium-fine-grained, dark grey-coloured, can be laminated in the finer varietiesand display dark veins (synsedimentary sills)and spatitic calcite veins crossing the stratum.Petrographically speaking, they are classifiedas hybrid arenites and biocalcarenites (Fig. 14).They are mainly made up of an intrabasinalcarbonatic component formed by foraminifers’shells with corals, brachiopods and echinoidsfragments. Grains of quartz, feldspars, and

phyllosilicates and siliciclastic rock fragmentsare also present, but subordinate. The cement,made up of spatitic calcite and micrite films,results to be undoubtedly more abundant thanin the Pietra Serena and causes the rock to becharacterized by a low imbibition coefficient(0,2-0,6 %).


The compositional and physical-mechanicalcharacteristics suggest an employment ofColombino and Albarese in flag-stones andexternal paving even subjected to intensetrampling. On the contrary, the Pietra Serenaresults to be more suitable for externalcoverings and architectonic manufacture or forall indoor employments, the last representingthe ideal collocation.

Historical examples of the Pietra Serenaemployments can be found in all the Tosco-romagnolo Apennine valleys. We can mentionas an example the Fortress (Fig. 15) anddefensive walls with the Fiorentina andBolognese doors , designed by Sangallo inFirenzuola, Palazzo Alidosi in Castel del Rio,Palazzo dei Capitani in Palazzuolo sul Senioand the Santa Maria Assunta Basilica in Bagnodi Romagna (Bargossi et al., 2002a).


Fig. 13 – Photomicrograph of Pietra Serena, a fine-grainedlithic arkose showing a quartz-feldspar component (N//).

Fig. 14 – Photomicrograph of Colombino and Albarese,very fine-grained calcarenites characterized by an abundantbioclastic component and by a subordinate siliciclasticcomponent (N//).

Moreover, we would like to remember thatsandstones called «Masegna», coming fromPiancaldoli and Marradi were employed in theBolognese area and that the so called«Macigno» sandstones were employed inFaenza in the Zauli-Naldi House and in Forlì inthe XVII century Orsi-Mangelli Palace(Rodolico, 1953).

Whenever they are employed, sandstones,like all worked stone materials, are subjected tothe action of disturbing agents of various natureand origin: mechanical, physical and chemicalactions such as the oxidation, hydration andacid aggression phenomena and those made bybio-deteriorating agents. All these processestogether can produce during time not onlymodifications of the aesthetic characteristics ofthe manufacture, but also a decay, which

sometimes is no more reversible, of thetechnical properties. Following consequencesmainly consist in exfoliations and detachmentsdue to swelling, along strata fissuring andcracking, turning into sand and efflorescences.

H) The Gessoso-solfifera Formation

The «Vena del Gesso» Selenitic Gypsum(Bologna, Ravenna)

Torriana (Rimini) Selenitic Gypsum

GEOLOGICAL SETTING

The selenites belong to the Gessoso-solfiferaFormation, outcropping roughly continuouslyin the Bolognese and RomagnoloPedeapennine and in isolated strips in theReggio Emilia and Rimini hinterlands. Thisformation originates from the evaporiticenvironment typical of the Messinian periodand is subdivided in one selenitic facies,developed in the Vena del Gesso Basin, andanother balatino-clay-solfiferous one,characterized by microcrystals and sandygypsum grains. The selenitic facies is made upof a series of gypsum strata (with maximumthickness up to 20 meters) separated bybituminous, thickly laminated claystoneslevels; characteristic is the typical dispositionof twinned gypsum crystals, the appearance ofwhich gives rise to the names «swallow tail» or«arrow-head», with tail points upwards(«Regola del Mottura»).

MINING ACTIVITY

The main quarries were located along the socalled «Vena del Gesso», mainly in Romagnain Brisighella, Borgo Rivola and BorgoTossignano and in the Bolognese area in Casteldel Britti, il Farneto, la Croara and ZolaPredosa. We should also mention theEpiligurian evaporitic deposits with the«Montebello di Torriana» quarry near to theSan Marino Republic, which brings out a verygood macrocrystalline gypsum nicely yellow-silver-coloured, much sought-after forsculptures and ornamental works, and the


Fig. 15 – The Fortress, Firenzuola (Firenze). The defensivewalls fortress, nowadays the Firenzuola Commune seat,built at the end of the XV century in Pietra Serena diFirenzuola following the plan by Antonio da Sangallo.

«Vezzano sul Crostolo» quarry in the ReggioEmilia province with blocks and scatteredreworked (clastic) gypsum crystals, amongwhich the sericolite variety can be found.


Gypsum, bihydrate calcium sulphate, showsa perfect cleavage, a vitreous aspect whichlooks translucent, porcelain-looking orsericeous depending on the variety. In fact,different varieties have been recognized:macrocrystalline, microcrystalline, sericolite,balatino and alabastrine. The macrocrystallinegypsum (selenite), is made up of clear,centimetric to decimetric crystals, swallow tailor arrow-head twinned, bearing clay impuritiesamong the interstices (Fig. 16).


Since the Roman age, selenite interested theurban work trade in Faenza, Imola andespecially in Bologna where an importanttheatre of Republican age was widened duringthe Neronian age by construction of a series ofradial walls in selenite. During the UpperMiddle ages we had the first seleniteemployment as cutting stone in the first wallcircle which brought to Bologna the name of

«silver city», very probably dating up toTeodorico times. During Common age gypsumblocks were re-used for the basements and thefoundations of the numerous Bolognese towers(Fig. 17), for rivers’ embankments, pillarswood basis, door-posts, window-backs,archivolts, supporting corbels and capitals.

The main deterioration morphology isrepresented by a differential deterioration dueto both the compositional and structuralheterogeneity of the stone, withmacrocrystalline gypsum crystals embedded ina clayey, easily alterable matrix. In the back-draft portions, crusts and concretions of limitedextension have been detected, preferentiallydeveloped in an orthogonal direction withrespect to the surface, so to assume a stalactiteor stalagmite-like shape.


Fig. 17 – Garisenda Tower (Bologna), XII-XIII century.The foundations, the basement covering and the archivoltare realized with large selenite blocks. The maindeterioration morphologies are represented by differentialdeterioration and superficial karren erosion.

Fig. 16 – Photomicrograph of selenite, showing a gypsummegacryst, arrow-head twinned (N//).

i) The Montecodruzzo Stone (Cesena)

GEOLOGICAL SETTING

Outcrops belonging to the Messinian«Gessoso-solfifera» Formation of balatino-clay-solfiferous facies have been mined alongcenturies to be employed in local building tradein the Cesena hinterland between the Savio andPisciatello river valleys. They are grey-coloured, brecciate-looking limestones anddolomite-limestones interested bysynsedimentary sliding and associated tobalatino and seletinic gypsum.

MINING ACTIVITY

The quarries which provided these brecciateMessinian limestones are located inMontevecchio, Monteaguzzo (Il Sassonelocality), Montecodruzzo (La Greppia locality)and Fosso di Ca’ Spinelli.

The Montecodruzzo quarry in Gorgoscurolocality brought up the Gorgoscuro limestone,so called by Veggiani (1964), and attributed byR.E.R. (1982) to the Lower Pliocenecalcareous-arenaceous Olistotromes.


They are brecciate whitish-coloured marlylimestones, with elements made up ofaphanitic limestone (micrite), fossil micro-fauna free, which almost always include smallgypsum plagues or crystals, plunged in amarly-calcareous cement where sometimeswe can find scattered quartz and mica grains(Fig. 18). Some of these elements show alumpy structure with small gypsum plagueinclusions and thin greyish and greenish clayveinlets.


The Cesena hinterland limestoneexploitation goes back to a remote age, but itsmaximum development occurred in 1400 and

1500 during the domination period ofMalatesta, who wisely used this local stonewhich resulted to be quite resistant and tough.In many localities of the Cesena hills(Montecodruzzo, Longiano, Montiano,Montevecchio) this limestone has mainly beenemployed in poor art works such as sinks,drinking troughs for livestock, rural housesbenches and corners, as well as in modestpublic works. The same material has beenfound employed in Cesena, with a decorativestructural usage, in columns, capitals,basements and architectural friezes ofreligious buildings and nobler palaces.Realized in Montecodruzzo limestone are thehistorical hall and the staircase of theMalatestian Library, the San Francescomonastery columns, the Santa Tobia lateralchapel of Duomo and columns and archivoltsof the Albizzi palace in Cesena.

The first cause of its deterioration is theworking the stone has suffered. Since it is arelatively soft limestone, it was workedmanually by tools such as axes or cleavers,while for the stronger parts hammer and bitwere employed. This led to microcracksformation, which meteoric alteration enhancedcreating true exfoliations and disgregation ofthe material.


Fig. 18 – Photomicrograph of the Montecodruzzo Stonewhere dusty micritic fragments are visible, cemented byskeletal, syntaxial gypsum (N//).

L) The Sasso Marconi Sandstone (Bologna)

GEOLOGICAL SETTING

The Intrapennine Bolognese Basinsandstones belong to the Epiligurian Domain.They are Pliocene shallow marine depositswhich at the bottom consist of clays with marlylimestones and laminated limestonesintercalations. After a gap, the sedimentationrestarts in the lower Pliocene with terrigenouspartly continental and partly fan-delta depositsre-elaborated by waves.

MINING ACTIVITY

The Sasso Marconi Sandstone was minedexclusively in the Sasso Marconi territorysouth-western of Bologna. In the area, made upof a huge arenaceous block of delta depositsbelonging to the Pliocene Intrapennine Basin,two quarries have been detected, anunderground one against Monte Sasso on theright bank of the Reno river, the other one openair on Monte Mario in Battedizzo, a SassoMarconi’s hamlet. The rock was mined bymanual systems using hammers, bits andwedges, with a documented activity betweenthe XIII and the XVII century. This miningactivity gave rise to a wide local market relatedto the realization of architectural anddecorative elements for palaces façades andchurches in the city of Bologna (Esposito,1999).


The Sasso Marconi sandstones can beclassified as terrigenous arenites passing intomedium-grained hybrid arenites with plane-parallel stratification, crossed laminations andthin clay and conglomeratic intercalations,showing yellowish colour and scarcecementation (Fig. 19). The calciclasticcomponent is constituted by micritic rockfragments and spatitic calcite. Bivalves andforaminifers fragment are also present. Thesiliciclastic component is mainly made up ofquartz, K-feldspar, plagioclase, oftenchloritized biotite, muscovite and fine-grained

magmatic, metamorphic and siliciclastic rockfragments. The cement, which doesn’t occludethe interstices between grains, is made up ofspatitic and micritic calcite and lookspigmented by iron oxides.


The Sasso Marconi Sandstone together withthe Varignana Sandstone has found largeemployment in the city of Bologna between theXIII and XVII century. The sandstonerepresented in the past the main buildingmaterial employed in the historical Bolognesebuilding trade, since it was easily available inthe area, «docile» for the chisel, and brought tothe city with low energies waste. Whole stone-cutters generations have mined the sandstonefor all different usages. The stone had the dutyto dignify the building and therefore itsemployment was mainly directed towards theunderlining of the building elegance, nobilityand importance; the stone was often reserved toframes, capitals, columns, carved cornices,doors and windows fastigia (Grillini, 1998).

These sandstones result to be characterizedby high imbibition coefficient (3,8%) andporosity values, with a scarce cementationdegree. These characteristics can give rise to


Fig. 19 – Photomicrograph of the Sasso Marconi hybridarenite showing a subrounded carbonatic component (N//).

intense deterioration phenomena whenevermanufactures are exposed in outdoorenvironment and can interact with beating rainand rising humidity. The deteriorationmorphologies of these sandstones are similar tothose described for the Varignana Sandstone, towhich the reader is referenced.

M) The Spungone Calcarenite (Forlì-Cesena,Ravenna)

GEOLOGICAL SETTING

The «Spungone» constitutes discontinuouscalcarenite bodies aligned in a compositehorizon which is associated to the LowerPliocene clayey successions, between theMarzeno and Savio river valleys. It can beplaced at the base of, or interbedded to, thePliocene Argille Azzurre formation, belongingto the Umbro-romagnolo Domain. It is alithostratigraphic unit in which bioherma facieswith biologically-built limestones can berecognized as well as biostroma bringingorganogenous fragments, which have beenmobilized from pre-existent calcareous bodies,and siliciclastic materials. Remains of thisancient submerged reef, which resistance toerosion gives rise to marked and clearly visiblerelieves, with particular shapes emergingamong the surrounding hills, are present in theFaenza area eastern of Lamone approximatelywhere the «Vena del Gesso» ends, and developnearly parallel to the via Emilia, interestingdifferent localities (Ceparano, Castellacciodella Pietra, Cerreto, Rio Cozzi, Bagnolo diCastrocaro, Sadurano, Rocca delle Caminate,Meldola, Teodorano, Fratta Terme, MonteCasale, Bertinoro, Capocolle).

MINING ACTIVITY

The word «Spungone», dialectal neologismfrom «spungò», which reminds of a white-yellowish-coloured rock and plentiful spongydue to the cavities abundance, is still used inthe scientific literature. In the Faenza area theSpungone is also called «albanello», «pietramora» or «pietra della Samoggia».

The Spungone mining activity has developedsince ancient times in all the hilly romagnolaarea bounded by the Lamone and Savio valleys.

Also in the Rimini hinterlands, Pliocene-aged calcareous tuffs similar to the Spungonehave been mined in the «Colle di Covignano»area.


From a lithological point of view, theSpungone bioherma facies are made up oforganogenous limestones very rich in fossilremains, among which calcareous alga(rodolites), foraminifers (nummulites andAmphistegina), bryozoans, molluscs(Pectinidae, Ostrea and brachiopods) andechinoids, embedded by micrite (Fig. 20).

The biostroma facies are made up ofbioclastic and hybrid calcrudites andcalcarenites with a variable cementationdegree.


The finding of Spungone-made tools(manual grindstones and millers) which can bebrought back to the late Bronze Age outlinesthat already the prehistoric populations, settleddown in the Lamone, Montone and Bidente


Fig. 20 – Photomicrograph of the Spungone, a biohermafacies made up of a bioclastic limestone (N//).

river valleys, somehow exploited this stone.Since the second half of and during all the Icentury B.C., the spungone was largelyemployed for the roman Faventia’s buildingart, in columns, capitals, architraves andorthogonal blocks for town walls. Even inForlì, the roman bridge «dei Morattini»,demolished in 1850, was mainly built inspungone; with the same stone were alsorealized the foundations of both the SanMercuriale basilica and bell-tower. During allthe Middle Ages it was used not only as re-employment material, coming from roman agearchitectures, but also as quarry material forother nature houses and buildings, such asfortresses and castles, churches andrepresentation buildings. Its employment waslimited to precise elements such as cornerashlars of noble palaces, columns basements,well-curbs, drip-stones and other plan elementsof churches’ façades, portals, bridges, andbasement structures of various naturebuildings. The numerous defensive strongholdsbuilt in the XIV and XV century assurrounding territories defence, have all beenerected on spungone spurs, using this stonealso as building material: examples of the latterare the Ceparano’s tower, the «Castellacciodella Pietra», the Castrocaro castle, the «Roccadelle Caminate» tower and the Bertinorofortress. We should remember above all theTerra del Sole stronghold, which Cosimo I de’Medici founded in 1564 following theharmonic establishment of Renaissance «idealcities», where the spungone represents the mostwidely employed stone (Fig. 21). Being cut inhuge squared hewn stones, it has beenemployed outdoor in the Porta Fiorentina,Porta Romana and in the corners of the brick-made town-walls. Rough-hewed spungoneblocks constitute the doors’ internal hangingwalls and the perimetrical cornices of theancient paving realized in river pebbles.Moreover, the spungone has been used forsculptural works, such as the two lionsoriginally located outside the Pretorio Palace,still in Terra del Sole. Last, we mention thebridge on Bidente in Meldola, of roman origin,

called «the Venetians’», since it was restoredby the Serenissima Republic between 1503 and1509; it is brick-made, but for the basal pillarsand the supporting arches, perfectly squaredhewn stones of spungone have been employed.

The rock’s consistence is not homogenous;in fact, we pass from extremely friablesituations due to sand prevailing, towardssituations of more solidity anywhere thecarbonatic cement and biologically-builtcomponents are predominant. The maindeterioration morphologies consist of pittingand alveolatization, with an accentuation of thetypical natural stone’s vacuole structure.Moreover, a differential deterioration, which inparticular outlines the stratified pseudoparallelstructure, has been detected. In the disruptedportions and in the stone’s alveoli, a biologicincrustation frequently develops, with musk


Fig. 21 – Porta Fiorentina (Terra del Sole, Forlì-Cesena),XVI century. Hanging walls built in bricks and squaredspungone blocks employed for the door covering and fordecorative elements (volutes and string-course). TheMedici coat-of-arms is carved in Pietra Serena.

and lichens and a diffuse occurrence ofvegetation such as caper-bushes and ivy-mantles.

N) The Varignana Sandstone (Bologna)

GEOLOGICAL SETTING

The Varignana Sandstone Formation belongsto the «Sabbie Gialle», which is part of theneoautochthonous basins at the front of theNorthern Apennines. Above the ArgilleAzzurre and the Spungone calcarenites, thePleistocene Sabbie Gialle Formation deposits,made up of yellowish sands with clayeyintercalations of marine and saltishenvironments passing to littoral yellow sandswith conglomerate beds. Laying on these,continental gravelly-sandy deposits appear,belonging to the Olmatello Formation, towhich the Monte Poggiolo Conglomerates ofthe Forlivese area, with the associatedPalaeolithic industry, are probably to bereferred.

MINING ACTIVITY

Sandstones belonging to the Sabbie Giallewere mined up to the XVII century, from somequarries located in the hilly area betweenBologna and Castel San Pietro. The firstquarries, of Medieval Age, were openedsouthern of the city of Bologna outside PortaSan Mamolo in Via di Roncrio and outsidePorta Castiglione between Santa Margherita alColle and Barbiano. Later, new quarries wereopened in the Varignana area, where two openair quarries can still be visited: the Malvezziquarry with a 15 meters wall and theCavalleggeri quarry with an about 3 meterswall. In these quarries, under semi-coherentyellow sands, sandstone strata occur, lithifiedenough to justify their employment as buildingstones (Pedrazzi, 1999).


The Varignana Sandstone are classified ashybrid arenites passing into calclithytes; their

grainsize ranges from fine to very fine, theyshow a typical yellowish colour and crosslaminations. The calciclastic component ismade up of micritic grains and spatitic calcitecrystals. Dusty yellowish-coloured micrite hasalso been detected. Bioclasts are represented byrelict structures of foraminifers’ shells, mainlyGlobigerinae. The siliciclastic component ismade up of quartz, plagioclase, K-feldspars(orthoclase and microcline), micas (biotite ±chlorite and muscovite). Metamorphic rocks’fragments, siltites, flint-stones, argillites, andbasic vulcanites’ ones are probably comingfrom the Apennine Ophiolites dismantlingprocesses. Accessory minerals are representedby garnet, epidote, spinel, pyrite, glauconite,zircon and apatite. The matrix and the cementare mainly carbonatic but they don’t totallyobstruct the rock porosity (Fig. 22).

In the Cavalleggeri quarry, flat-tilesconglomeratic intercalations, up to decimetricthick, can be observed, characterized by abimodal grainsize distribution and a grain-sustained structure. The conglomeratic clasts’dimension is 2-3 cm; they mainly constitute ofmicrites, biomicrites, siltites and spatites, whilethe fine-grained arenaceous «matrix» presentsthe same petrographic characters of thesurrounding rock (Fig. 23).


Fig. 22 – Photomicrograph of the Varignana Sandstone, avery fine-grained hybrid arenite with random foraminifersshells (N//).


The employment of these yellowishsandstones in the Bolognese territory has beendocumented since the VIII and VI centuriesB.C., in the proto-«felsinee» («from Bologna»)oriental stelae employed as funerary ensigns,and in the monolithic cylindrical VII centuryB.C. altars, finely decorated. Since the XIIIcentury the Varignana Sandstone has beencommonly employed in buildings, as forexample in the communal Palace’s porticopillars, where sandstone ashlars were alternatedto brick rows, and in the monumental windowby Alessi. In 1390 in the Loggia dellaMercanzia, sandstones capitals were built;yellow sandstones were largely used in thePalazzo Bevilacqua ashlar, in the Palazzo delPodestà façade (Fig. 24) and in the Fava(Sabetta et al., 2001-2002) and Ghisilieri’sPalaces courtyards. The sandstone employmentcontinued till the XVI century, in theBentivoglio, Malvezzi-Campeggi, Fantuzzipalaces, in Palazzo Poggi University seat, inthe Archiginnasio portico and in the PalazzoBocchi ashlar-work (Rodolico, 1953).

The Varignana Sandstone with highimbibition coefficient values (5,4%) and scarcecementation degree, when exposed to beating

rains and rising humidity, results not to be along lasting material. The deteriorationmorphologies which have mostly been detectedare concretions and black crusts. Two are themain processes attacking these sandstones:dissolution of part of the carbonatic componentand subsequent recrystallization on the surfacein protected area which are not washing-awaysubjected (back-draft zones). Rain andcondensation water, particularly enriched inCO2 and H2SO4 (the so called acid rain),penetrate the sandstones, causing thedissolution of minimum amounts of the stonesoluble components, which are then draggedand re-deposited on the surface duringevaporation. The calcium carbonaterecrystallizes again as calcite, but above all ascalcium sulphate (gypsum). In this way a


Fig. 24 – Palazzo del Podestà (Bologna), XV century.Frontal arcade with surface made up of bricks showing thetypical bolognese finishing, the so called «sagramatura»and architectural frameworks, finely carved ashlar andleaning columns built in yellow Varignana sandstones.

Fig. 23 – Photomicrograph of the Varignana Sandstone(Cavalleggeri quarry). Rounded calcareous pebbles with aninterstitial arenaceous component (N//).

black-coloured strong concretion (black crust)has formed, developing orthogonal to thesurface, which, at the recrystallization time,encloses smog bearing waste-gases unburnedproducts and atmospheric particles.

Other recurring morphologies are due to theparticular sedimentary structures present in theyellow Varignana Sandstone, which constitutepreferential detachment surfaces or planes. Infact, the heterogeneous grainsize, alternating«fine-grained» to «medium-coarse-grained»sandy portions, often determines a laminatedstructure and the remarkable occurrence of«conglomeratic lenses» with siliceous,carbonatic and siltitic clasts, ranging from 20 to30 mm in diameter, well-rounded clasts andpseudoparallel lying. These, during time, canrepresent cutting surfaces or planes when therock has been put running. Along thesemineralogical-petrographic and sedimentarydiscontinuities, characterized by differentporosity, the meteoric acid water can cause aselective dissolution of the carbonatic cement,with a consequent loss in cohesion andfollowing detachment of the conglomeraticportions, with the formation of some typicaldeterioration morphologies such asalveolatization and pitting, involving vacuolesand pores of different shape and size.

O) The Labante Ttravertine (Bologna)

GEOLOGICAL SETTING

Western of Vergato (Bologna), on the rightside of the Reno valley, the BismantovaSandstones Formation is interested by deepcracks from which springs gush out. Thecalcium bicarbonate waters, in a subaerialenvironment, give rise, by precipitation, toencrusting Holocene limestones (calcareoustuffs, travertines), cementing the vegetationnext to the spring.

MINING ACTIVITY

Ancient proofs reveal that a travertine wasmined in Santa Maria di Labante locality

nearby Vergato. The quarry, now dismissed,brought up a porous stone called travertine orPietra di Labante, even if less compact ifcompared to central Italy travertines. Inaddition to the Santa Maria di Labante quarry,there’s another one near Castel d’Aiano,always occurring near to springs, streams andwaterfalls rich in carbonatic waters.


It is a calcareous Tuff, white-yellowishtending towards rosy coloured, characterizedby a fibrous concretion-made structure, passinginto vacuous, with an undistinguishablestratification where you can neverthelessrecognise thin bands differentiated byimpurities concentrations, mainly vegetables.The cavernous aspect is partly due to thevanishing, by decomposition, of vegetablesfragments encrusted by calcium carbonate. Thecarbonatic component is made up of dustymicritic calcite passing into spatite on vacuolesboundaries (Fig. 25).


Since the Etruscan age, the local travertinewas mainly employed in the sacred places ofsettlements, in temples and especially in tombs.


Fig. 25 – Photomicrograph of the Labante travertine (NX).Micritic dusty crystals forming a concretion-made structurewith abundant macropores.

Very probably, Etruscans considered it a veryrich and valuable material, since it was difficultto find. In the Etruscan city of Misa, in theReno valley, traces of paving in squaredtravertine blocks, houses foundations, columns,stelae and cippi have been found. At thewestern and northern sides of the city twosepulchres are displaced, with large case tombsin travertine slabs, sometimes surmounted bytravertine cippi. We also remember theEtruscan necropolis of Giardini Margherita inBologna, with small sepulchres and animportant case tomb double-weathered coveredbuilt in travertine blocks, which has beenreassembled on the finding place.

This travertine, cut into blocks, has also beenemployed, up to the 60s, in the mining areasurrounding localities in buildings such aschurches, bell-towers and cemeteries (Fig. 26).

The deterioration morphologies in travertinemainly refer to black crusts and to a diffusebiological growth. The black crusts especiallydevelop in moulding back-drafts causing,during time, real concretions, orthogonal to thesurface. The biological growth, characterizedby lower plants such as musk and alga,develops in travertine vacuoles where soil, dustand meteoric water collect, creating a fertilesoil, a real «pedologic substrate».

CONCLUSIVE REMARKS

Descriptive reports on dimension stonesdescribed in this paper allow us to put forwardsome conclusive remarks that, according to us,could have some importance both in the miningactivity exploitation and in the cultural heritageand architectural fields.

Information which have been collected aboutancient quarries, where dimension stonesemployed in historical cities were mined,represent a useful knowledge base for arthistorians and for those who have to makerestoration interventions both conservative andsubstitutive towards the monumental andarchitectural heritage. We stress that dimensionstones represent unique materials which shouldbe jealously protected otherwise it would no morebe possible in the future to carry out substitutionswith original stone elements. For additionalgeological and petrographic data and physical-mechanical characterization of the materials thereader is referred to Bargossi et al. (2001).

The knowledge of present-day productivedistricts in the dimension stones field in thissector of the Emilia-Romagna and RomagnaToscana regions, for what concerns mainlysandstones and secondarily selenites, shouldgive rise to the consciousness that thegeoresources exploitation, provided thatachieved with respect for the environment andin harmony with the mountain territory,represents a unique economic source forcommunities which otherwise would bedepressed. This kind of activities must beunderstood and encouraged in order to improveboth mining activities and dimension stones


Fig. 26 – Chiesa di San Cristoforo in S. Maria di Labante(Vergato-Bologna). Hanging walls and corner hewn stonesof the bell-tower and of the church realized in Labantetravertine. The basement and the bifora-windows are builtin Castel d’Aiano Sandstone.

working, and supported to obtain petrographicand physical-mechanical characterization data,absolutely necessary to gain the EuropeanCommunity quality-mark «CE Mark». Thesedata are essential to bring on the marketproducts of guaranteed quality which could bechosen for the correct employment accordingto scientific criteria; in order to guaranteelasting, every rock must be employed insituations consistent with its specificcharacteristics.

Regarding the territory valorisation shouldalso be encouraged those activities that,referring to «geosites» quarries and«architectural emergences» monuments wheredimension stones have been employed, realizedidactic or tourist-cultural itineraries in order to directly enjoy the cultural and landscapeheritage. We should keep into mind that somequarries’ fronts showing particular geologicalstructural situations must be protected andpreserved in order to make it possible foreverybody to behold and study them.

Finally, a further element that shouldn’t beneglected is the preservation of the art ofcarving the stone, art which in our territory hasancient traditions going back to the «magistrimuratores», coming from the Lombardia-Ticino area and better known as «Comacinemasters», of Latin culture, acknowledged andprotected by the Rotari and Liutprando edict.Periodically many efforts have been made tohand down this tradition, carrying out coursesof building restoration where the manualworking techniques of sandstones were treated;nowadays still persist stone-cutter artisansworking in our Apennine valleys. Also in thiscase, we are talking about unique activitiesstrongly bounded to the historical-culturaltradition of the territory which must absolutelynot be wasted; on the contrary they should beencouraged creating a permanent school forsandstone’s stone-cutters.

ACKNOWLEDGMENTS

We thank Andrea di Giulio who revised the paperwith constructive criticism. We are also grateful to

Gian Battista Vai for kindly reading the last versionof the manuscript with comments and suggestionswhich helped us to significantly improve it.

REFERENCES

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